This invention relates to a granulated filter having the capability for removal of very fine particles from suspensions. The filter is characterized partly by the efficiency in reusing the filter media through a backwash operation and partly by the favorable economy due to an extreme low filter bed depth.
Recent environmental requirements are leading the developments of new filtration technology towards the task of fine particle removal within the municipal sewage treatment field and the industrial wastewater treatment field as well.
The existing technique for filtration of fine particles is mainly based on membrane filters and/or cartridges. While the cartridges may have small particle sizes and low filter bed depths, the filter media can not be backwashed in regular sequences, they have low flow capacities and they can not be arranged for large-scale installations within reasonable investment cost limits.
Other filters in the market are those with granular filter beds. The filter media are usually sand in different mesh sizes, anthracite, dolomite, activated carbon, etc. These filter beds can mostly be arranged for backwashing either in sequences or continuously. The filter beds can be loaded with much higher flow rates than what is possible for the membrane and cartridge filters. Consequently, the granular filters are more economical due to the operation costs and investment costs as well. However, a substantial disadvantage is the fact that existing granular washable beds cannot be arranged for filtration of fine-particles. The physics of the granular beds, the filter arrangement itself and the washing procedure do not make the filtration of fine particles possible.